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HUG - here for all audio enthusiasts

Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings sub-forum is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.

The Moderators' decision is final in all matters regarding what appears here. That said, very few Posts are rejected. HUG Moderation individually spell and layout checks Posts for clarity but due to the workload, Posts in the Subjective Soundings area, from Oct. 2016 will not be. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

That's it! Enjoy!

{Updated Nov. 2016A}
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Working with the human ear: the proper evaluation of audio equipment incl. amplifiers

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  • Commanding a cone to vibrate

    I was having trouble with Pitch 2 and 3. I couldn’t tell. I was using the same PC as Pitch 1 but just couldn’t distinguish any difference. I tried again in more relaxed environment and with my laptop and I hear the subtle difference.

    Could an old soundcard or a speaker (built in Mono speakers) make the difference less obvious? I am not sure how a speaker functions to produce a 440Hz, but my guess is it needs to vibrate 440 times per second. If that is the case, then the speaker needs to vibrate or oscillates 443 times per second to produce the 443Hz. If this is a correct assumption, then how accurate can a mechanical cone that depends on magnetic force to create push and pull function against the surround and air accurate keep count of these numbers? Can we be sure that it actually would vibrate 443 or 440 times and not a plus minus of few beats?

    ST

    {Moderator's comment: ... because you would have created a time machine.}

    Comment


    • Differences

      I not sure what I should I say after listened pitch 3, anyway, I just write my feedback here.

      I tried to listen this pitch 3...I do not know how to say it..If only just the A and B separately I do not think I can detect the different. But if listen them side by side and keep repeating for few time, it is clearly that, both sing in different pitch. And by resting my ear for 30s and listen again for the 1st time, I am confused, then I must listen for the 2nd time and repeat for few time to be able to detect the difference. By listening the clip 1st few second, pause it, jump direct to the last few second, the difference is undetectable by me.
      "Bath with Music"

      Comment


      • Conclusion?

        Originally posted by keithwwk View Post
        ... If only just the A and B separately I do not think I can detect the different. But if listen them side by side and keep repeating for few time, it is clearly that, both sing in different pitch. And by resting my ear for 30s and listen again for the 1st time, I am confused, then I must listen for the 2nd time and repeat for few time to be able to detect the difference. By listening the clip 1st few second, pause it, jump direct to the last few second, the difference is undetectable by me.
        Surely what you're saying is exactly what this experiment is designed to illustrate - or do I misunderstand you?

        The point I am attempting to convey is that only when the two events (A and B) are presented 'adjacent' to each other in time with a negligible gap, can our extremely limited (but highly predictable) sense of hearing effectively tackle the analytical task of determining if A and B are the same or similar, or quite different. If I understand you, you have found that at around the switch between A and B you are able to readily detect that they are indeed different frequencies, but not easily or at all when they are not compared directly against each other. Is that correct?

        If it is, you have proved the very point: our ears are expert at making comparisons but only when we have the two stimuli directly set against each other.
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • Yes

          Originally posted by A.S. View Post
          ..... If I understand you, you have found that at around the switch between A and B you are able to readily detect that they are indeed different frequencies, but not easily or at all when they are not compared directly against each other. Is that correct?

          If it is, you have proved the very point: our ears are expert at making comparisons but only when we have the two stimuli directly set against each other.
          Yes Alan, you are right. That's exactly how I feel.
          "Bath with Music"

          Comment


          • Originally posted by keithwwk View Post
            Yes Alan, you are right. That's exactly how I feel.
            Well that's good. It proves that your ears and my ears (and indeed everyone else's ears!) work the same way. Very good at instanteous side-by-side comparisons, not very good at all at time-separated comparisons as I've shown throughout this thread.

            A vision comes to mind of bartering for fruit in a far-away street market. The seller has no scales but he does have a pre-made weight. It doesn't matter if it's in pounds or kg or even his own made-up weight system. He places this weight in his left hand and then the fruit you select in his right hand and does a little joggle with his hands. Which one is heavier and how much to charge? If you don't agree with him, he'll hand you his reference weight and the fruit and you can confirm for yourself. Humans are universally good at that sort of comparative measurement and can quite accurately resolve differences in temperature, sound, weight, texture, bitterness or sweeteness, frequency, colour etc. providing that we have something 'in the hand' to compare against.

            Thanks to everyone who contributed feedback. If nothing else, despite the wholly misguided armchair-expect criticism I have had over the amplifier comparison, I hope that I've illustrated the point that it is a very brave man indeed who would put his total trust in judgements about audio separated by minutes, hours, days, months or years. There is just one final observation to make, tomorrow.
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

            Comment


            • The "Harbeth Amplifier A-B challenge" - is now closed.

              Thirty days ago, we laid down a challenge (from post 58) to finally put to rest the all-too-frequent and unanswerable question here on HUG 'should I upgrade my amplifier' .....

              ...The objective of this thread on A-B amplifier comparison is to attempt to confirm (or not) that the millions of words written on the subject of 'amplifier sonics' are backed up by the reality of being able to hear the difference when cosmetics, features, brand name and variation in loudness are removed from the equation. Our position is that Harbeth speakers will work well with any credible amplifier performing to original specification. You need not be concerned that once you buy Harbeths you are on an unwelcome, expensive merry-go-round of electronic upgrades: you are not.
              A.S. ... let me repeat yet again: for reasons that we do not understand, it would appear that under instantaneous A-B switching driving Harbeth speakers, that amplifiers of broadly comparable technical performance and matched for gain are not readily distinguishable. That is not to say that 'all amps sound the same' under random, uncontrolled listening.
              The challenge offered an attractive gift for a person able to distinguish amplifiers under A-B testing:

              In anticipation that I may be surprised and for whatever reason the two amplifiers are readily and repeatedly distinguishable under the instantaneous A-B switchover, we have decided to 'provision' for the gifting of a pair of M40.1s in our financial accounts for the year end 31 March 2012. That means the will be no hard feelings at all from this side in the event we are proven wrong - which we hope we are because if one 'star performing' amplifier is revealed it will have been worth the cost. Other than actually drawing-out the circuit for the relay switch-over comparator I believe that I've done all I can and need to at this stage and await proposals.
              I provided a list of all the parts needed to make a relay comparator box (assuming the participant would not have confidence in my switcher) in this post here. This 'challenge' has been widely reported and discussed in specialist audio forums and has apparently had over 50,000 viewing hits. Scanning the threads shows that having started out with extreme hostility and incredulity, that led to personal attacks on my motives and integrity and finally the subject died long before the 31 day closing date.

              As this thread has shown, when humans are able to compare two sensory events with only the briefest interruption between them, our brain is capable of making reliable judgements. When a delay of more than one or two seconds is introduced, we find it much more difficult to make objective comparisons. So it is with sound. The essence of my comparison test is to reduce the time delay between switching from A-B to just that of the relays flicking over - as illustrated here, about fifteen thousandths of a second. Under these rapid-fire change-over conditions, differences (or not) should be audible between equipment such as loudspeakers, electronics, cables amplifiers etc..

              To my dismay, this simple, cheap and effective A-B comparative test suggestion caused a fire storm of outrage amongst certain audiophiles. Every line of attack was tried to discredit the concept before it was even tried-out: I am deaf; Harbeth speakers must be so poor that they are incapable of distinguising the self evident differences between the amps; the test was biased in Harbeth's favour; the relay switches were imperfect and would corrupt the signal somehow; the participant would be deliberately fatigued by the suggested 100 switch-overs*; the concept of A-B was a denial of human sensory nature and so on. We became aware that despite the dedicated audiophile's eager willingness to regurgitate manufacturer's techno-marketing babble about the technical minutia of this capacitor type or that, this transistor type or that, this cable type or that (all of which are electro-chemical specifics of the laboratory and PhD experts) rolling up the sleeves and actually assembling the switch-over box was admitted to be far beyond their constructional ability. Yet, in truth, a battery, a switch and some relays could be constructed to a satisfactory standard by an average high school physics student. Nobody who is unwilling or incapable of soldering a few bits of wire to a battery should be able to pontificate about electronic design. This disconnect from hands-on (across most/all areas of consumer electronics) sets-up the unpaid consumer as a marketing conduit for the upgrade-inspired manufacturer and has confirmed my worst fears about the impossibility of the average consumer separating technical fact from marketing BS. We've already covered that here. It's going to destroy this industry.

              We were extremely relaxed about almost every aspect of the comparison, and had a clean, blank sheet of paper with just two mandated requirements: the participant must drive the speakers through his (or my) relay change over box and the amplifiers must be level matched beforehand. How they were to be matched (what method? what frequency?) was negotiable. I assumed that the participant would wish to observe that measurement process and that I'd patiently walk him through it to allay any misgivings he may have about test equipment. In fact, everything except the relay arrangement was negotiable - the music, the location, the amplifiers to be used as A and B, which Harbeth speakers, cables, stands, music source, how many observers, scoring method .... absolutely every detail could be worked-through and agreed beforehand. I would have helped the candidate solder together his switcher if he so requested and I even considered a legal agreement (obviously at my expense) so that the outcome was binding on both parties - we handing a pair of free M40.1s to the lucky 'winner' or he graciously accepting that he could not tell the amps apart. I assumed that I would have laid-on and paid for a nice lunch and/or evening meal for participants and that the whole process would be undertaken in my normal relaxed, friendly way complete with a tour of this historic area. I did not expect the participant to pay a penny piece, except building the relay box (about GBP20-30) and I budgeted about GBP 250 for food/drink plus the cost of the M40.1s if they were handed over.

              What did we anticipate would happen, and what actually did happened?

              We anticipated that we would have to arrange a number of sessions of perhaps 2-3 hours spread over a week or so as participants brought forward their amplifiers claiming 'night and day' differences in sound. We'd measure them technically and then carefully adjust the replay levels so that each one was playing at the same loudness. Some internet chit-chat said that it would be easy to walk away with a free pair of M40.1s (any veneer, incl. rosewood) and then next day they'd be listed on Ebay, but as we didn't preclude that we could not have objected. We were told that there was absolute certainty amongst the die-hard audiophiles that they could, under sighted conditions, easily tell this amp from that. As the arguments raged, some were not so sure what to expect if the amps were directly compared under A-B conditions. Slowly the voices of objective, technically trained commentators came to the fore and reminded readers that all known public A-B comparisons had reached the same conclusions during the past thirty years: sonic differences diminish or disappear when the participant cannot see the electronic equipment just as I suggested at the outset. And so, the raging torrent of fury and disbelief slowly dried-up and then ceased.

              So, how many presented themselves as participants within the rules of the game, which mandated the use of the relay box? Not one single, solitary sole. Not one. I am so surprised. And furthermore, not one phone call, email, fax or letter from anyone connected with Harbeth sales or distribution. Not a peep. Business continued as usual.

              I have permission to present, unedited, the one email we did receive from the public but as this gentleman says, he would not permit the use of the relay switcher (and therefore he cannot be considered a prospective candidate) but he did have the courage to step forward. What he says summarises the audiophiles position:

              ..."I don't care what method other people use, my method that works for me is as described below; A-B-A-B with the whole track played each time.

              In my view 2-30 second swaps are a complete waste of time and only show up tonal differences, not difference in timbre, image or detail. I don't see the reason for limiting it to 30 seconds, as this proves nothing. For info, I tried my method out last night at a friends house using 4 amps and 100% was able to tell which one was which, as usual (3 valve 1 transistor). Now I am sure they don't all measure the same, but that is another point, all the amps were current and good quality (£2K to £6K cost).

              I listen to rock and techno fairly loudly.

              Lets be clear, I am not making or buying anything and I am not getting involved in me having any costs (other than travel) in this whole thing. I can supply amplifiers and cabling and if needed a decent source (either vinyl or CD). I don't believe in switch over boxes as they add extra masking, simple banana plugs on the speaker cables should be fine."
              Where do we go from here?

              As we said many posts ago, we respect and support all those who design, make and sell electronics. But we are not at all comfortable that this loudspeaker forum is used to provide unsubstantiated and unsubstantiatable opinions for electronic 'upgrades' none of which are necessary for getting the best from Harbeth's easy-to-drive speakers. Other speaker brands may well be amplifier sensitive. In our opinions that is sheer bad speaker design. Harbeth speakers are an easy, amp-friendly load. Full stop. End of story.

              So, we state yet again our view about the purchase of electronics ....


              '... the selection of an amplifier should, in our view, be based primarily on pragmatic issues of its durability and longevity, styling, features and facilities, brand reputation, technical specification (power, hiss etc.) and after-care service back-up until such times as the claimed night-and-day 'sonic differences' can be validated as real, not illusory under non-sighted, controlled listening tests. If 'sonic differences' can be positively identified under controlled conditions then, obviously, they should be added to the list somewhere'.
              Please do not breed discontent amongst Harbeth users by claiming that changing electronics will give them a 'night and day' sonic experience. It won't, but it may give them prettier, more reliable electronics with better features all of which may indeed be worth paying for. Visit your dealer: he'll tell you the inside story behind an electronic product/brand, the one you don't read about in forums. Base your purchase decision on hard face to face facts from your dealer. Go listen for yourself but be sure that you are listening at exactly the same level, matched to 0.1dB to accurately compare sonics or just buy what you like the look of and are assured has a proper service backup. But please don't buy based on unsupportable claims about wonderful, earth shattering sound differences.

              Conclusion: I am shaken after experiencing first-hand the knowledge vacuum between how audio/sound/business/human nature actually works and how certain dedicated audiophiles think it works and how loud they shout to defend their beliefs. It now wouldn't surprise me if there are internet chat forums discussing the ins and outs of neural surgery amongst people who have never held a scalpel. This is madness. To make technical purchasing decisions, to discuss intricate technical parameters and to influence others, you have to have to have baseline technical knowledge by whatever means you acquire it, formally or informally. Plus a good deal of common sense. It's a denial of reality to believe that you can comment meaningfully on neuroscience because you once visited a butchers shop. That's the state of affairs in high end audio though.

              I remain dedicated to doing whatever I can to illuminate how audio really works for the benefit of great music at home (example today here) whether the facts are palatable or not. You can always look away.



              *Very few commentators bothered to check what I actually wrote here. I did not define exactly how long the participant could listen to A before switch to B (and vice versa). I listen in short burst of perhaps 10 or 20 seconds then switch; I do not listen for more than 30 minutes or so at a session to avoid fatigue. 100 switch-overs could take as little or as long as the participant wanted.
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • You just might be right ....

                Hi Alan

                Indeed, the offer of your challenge has lapsed with not a single soul taking up the gauntlet! Like many a curious bystander, I was hoping someone would actually accept your challenge so that there would have been an experiential anecdote that would have doubted or validated your strong belief that under controlled circumstances the selection of amplifiers of broadly comparable technical performance and matched for gain are not readily distinguishable, one from the other.

                Like many, such a proposition seemed almost insanely preposterous to be believable and evoked reactions ranging from mild indifference to heretical swearing! Yet not a soul stepped forward to prove you wrong. While it would be wrong to deduce or infer from this inaction that your proposition is therefore right, I have deep respect for your courage in holding fast to your beliefs! While I have not always agreed with everything that you have said in my many years as a forum member, I am increasingly inclining to the view from my own experience (almost one score years) that you are largely correct in evangelising such a view, contrarian as it might at first blush sound.

                It is interesting to note from your many posts that you have candidly admitted that you don't fully understand the rationes behind this view which might empirically explain why this is so, perhaps the answer might lie in the complex field of pyscho-acoustics and the cerebral hemispheres of that grey matter which lies between our ears. Perhaps someday, somewhere and somehow we would have the science (and art) to finally put to rest this phenomenon, proving beyond reasonable doubt that the electronics, so long as of competent design and quality, does not make such a big difference as audio manufacturers and audiophiles make it out to be. When that day of pragmatism arrives (and I hope my heart will still be beating and my ears, capable of hearing), I think we will all be closer to the main objective of really enjoying music instead of chasing our tails for that elusive amplifier that powers our beloved Harbeths!

                Listen to this clip which was recorded using two microphones positioned approximately where our ears might be to experience the wonderful miracle of the human mind in how we hear, anlayse and perceive sound in order to create the sense of ambience and depth and consequently, the realism of a musical event. Although earphones are recommended, you can nevertheless experience the holographic effect with your Harbeths!

                http://www.youtube.com/watch?v=IUDTlvagjJA

                Comment


                • Lights down and a glass of wine

                  Originally posted by denjo View Post

                  Indeed, the offer of your challenge has lapsed with not a single soul taking up the gauntlet!

                  It is interesting to note from your many posts that you have candidly admitted that you don't fully understand the rationes behind this view which might empirically explain why this is so, perhaps the answer might lie in the complex field of pyscho-acoustics and the cerebral hemispheres of that grey matter which lies between our ears. Perhaps someday, somewhere and somehow we would have the science (and art) to finally put to rest this phenomenon, proving beyond reasonable doubt that the electronics, so long as of competent design and quality, does not make such a big difference as audio manufacturers and audiophiles make it out to be.
                  It is indeed surprising - even more so given that any challenger could get the prize, but with no price to pay for losing, other than travel costs, I guess.

                  On the cerebral thing - I am convinced that this is what is "messing up" things. My system sounds best to me, when the lights are down low, and after a couple of glasses of wine or a good single malt. Nothing has changed in "real" terms, but what happens inside the brain is more real to me than what is "real" outside in the room.

                  And when I change electronics to a highly recommended (touted?) and more expensive unit, I "hear" better sound.

                  I now have realized this, and prefer the lights down low/glass of wine route.

                  Comment


                  • Shaky corporate foundations

                    Originally posted by Kumar Kane View Post
                    It is indeed surprising - even more so given that any challenger could get the prize, but with no price to pay for losing, other than travel costs, I guess...
                    It is surely the most disappointing (failed) 'experiment' of my career. Yes, nobody stepped forward except the one I mentioned and as he would not play by the rules (didn't accept the switch-over box), he debarred himself. I heard recently that a UK amplifier manufacturer was much aggrieved by the proposed comparison. I can only imagine that he fears (or anticipates, or knows) that the outcome would not be good for sales if, as I postulate, when amps are compared under controlled conditions the big reported sonic differences "diminish or disappear", to quote myself.

                    That is a barmy, short sighted way of looking at the marketing of quality audio products. As I said, what I would do as an amplifier marketeer would be to promote the real, tangible benefits of the brand: quality components, careful consideration of longevity in design and assembly, company reputation for after-care, a buy-and-forget (almost) forever approach .... these are all real benefits and worth paying good money for. Fabled 'sound quality' is a completely nebulous, intellectual dead end. As dead an end as the sort of utter cobblers that is used to sell anti-wrinkle cream to women. No marketing campaign - no viable business - should pivot its entire existence upon such a wiffly-waffly, easily disproved (under controlled tests) promotional strategy. I'm so sure of this that if I were tasked with bringing a quality audio amplifier to market, I'd set myself the challenge to never introduce 'sound quality' into its promotion and I'm confident that it would be a sales success solely by concentrating on the real-world user's benefits. Promoting superior sound quality (or even strong sonic personality) of electronics is nothing more than the marketeer scraping the very bottom of the barrel for something new to say to a consumer daft enough to be seduced by sweet words that he wants to hear.

                    Sure as night follows day, when this subjectivist road if fully walked, (because there is nothing more to say, the would-be consumer has lost interest) there will eventually be a complete reversal in the media and it will be fashionable again to say ... 'You know what? We were all kidding ourselves about that subjectivist stuff. Let's get down to basics again ....'

                    Bank on it.
                    Alan A. Shaw
                    Designer, owner
                    Harbeth Audio UK

                    Comment


                    • Global GDP need consumption

                      Originally posted by A.S. View Post
                      to a consumer daft enough to be seduced by sweet words that he wants to hear.

                      Sure as night follows day, when this subjectivist road if fully walked, (because there is nothing more to say, the would-be consumer has lost interest) there will eventually be a complete reversal in the media and it will be fashionable again to say ... 'You know what? We were all kidding ourselves about that subjectivist stuff. Let's get down to basics again ....'

                      Bank on it.
                      I am not so sure I would bank on it, Alan. Human nature being what it is, there are so many people out there that are waiting for someone to tell them what they want to hear, so they can indulge in retail therapy. Marketers build careers doing just that in the consumer products and services industries. Global GDP would crash if people stopped listening to their pitches. Maybe it would be a one time correction, and be a lot better for the planet in the long run, but I don't see it happening.

                      Comment


                      • The Failure of Audiophiles is Your Success

                        Originally posted by A.S. View Post
                        It is surely the most disappointing (failed) 'experiment' of my career.
                        If you think of the challenge and the response as part of the whole experiment, then the (non)response of the audiophile community to your challenge, Alan, makes your experiment a success. Suppose some audiophile (in England, to minimize travel costs) really and truly, in his heart of hearts, believed with great certainty that he could hear differences between two amplifiers (under controlled conditions). Would he not have taken up your challenge? Why wouldn't he? So (argument by contraposition), from the total nonresponse to your challenge (to your experiment) we may infer that no audiophile (at least in England) really and truly, way deep down, believes with any certainty the garbage about amps. In my opinion, that's one very, very successful experiment.

                        Bruce

                        Comment


                        • The father of 'amplifier differences'?

                          Originally posted by Euler View Post
                          .... we may infer that no audiophile (at least in England) really and truly, way deep down, believes with any certainty the garbage about amps. .
                          On many occasions, after carefully level matching between different amplifiers I am unable to tell any difference. Having said that, I am inclined to prefer the sound of some amplifiers played under the normal listening level.

                          If anyone spewing garbage about amplifiers sounding difference, then Norman H. Crowshurst should be the first one to be blamed for making such a claim.

                          Two amplifiers of conventional design were taken and modification made to bring their design into the line of mathematical theory….AB checks were conducted between the amplifiers using the original circuits and the revised feedback circuit. A difference was quite noticeable …particularly..when wind instruments… or string instruments are played. These experiments certainly seemed to have uncovered at least some of the major differences that can exist between amplifiers with equally good specifications – differences that do not show up, at any rate, in the standard method of specification. These are, in fact, defects that are not in the books!
                          - Norman H. Crowhurst.
                          ST

                          Comment


                          • The importanc of amplifier features

                            Originally posted by Euler View Post
                            In my opinion, that's one very, very successful experiment.
                            I agree.

                            What will happen though is that it will be buried in new threads/posts with the passage of time, and the same tedious discussions (about the love for this amp or that) will continue, even on this forum.

                            In other fora of course, the debate will continue to rage, the population at large has no clue about this initiative from Alan.

                            Oh well, the internet is a free medium, and at least, no trees are cut down to make paper:-)

                            A few years ago I decided to simplify my system, and settle down with a now ten year old Quad 909. I love it and I hope it will last at least another ten years, if not more. I got my C7s just last year because I was moving into a larger house that needed their heft, and the discussions on the forum, and the C7 capabilities underline how sensible the decision was.

                            At 140wpc the 909 is more power than required, but that isn't reason enough to change amplifiers. And the ten year old Quad 99 preamp that feeds the 909 is also brilliant for its feature set - tone controls, and a phone stage that can take moving coil as well as moving magnet inputs. Even today, it isn't easy to find one with the combination of features it has.

                            Comment


                            • Being led by the nose

                              Originally posted by Kumar Kane View Post
                              I agree. What will happen though is that it will be buried in new threads/posts with the passage of time, and the same tedious discussions (about the love for this amp or that) will continue, even on this forum....
                              Whilst my (failed?) experiment has been a disappointment* what has been even more noteworthy is, as you suggest, the continuous stream of those eulogising about this amp over that amp - even here on the HUG. We simply cannot understand the force that drives people to utterly ignore the thrust of our considerable input on this debate (that amps must be compared under controlled conditions) and then tell the world, here, that under uncontrolled conditions that they've just had a night and day experience substituting amplifiers. Of course they will hear a difference! That's a given! But that difference is not likely to be the amp itself, it's the result of comparing two uncontrolled events. How many millions of words and visual/musical examples do I have to make to hammer home once and for all the concept that the human brain is very, very, very easily duped?

                              I'm beginning to ask myself why I actually care about this. It certainly isn't because I want to dissuade folks from visiting their hi-fi dealer and spending wads of cash - quite the opposite. It's because this nonsense is endemic of a breakdown in society of rational thought, the ability and willingness to use one's own common sense. This failure of independent thinking, and the willingness to be led by the nose by persuasive opinionated leaders has cost, and continues to cost, human lives.

                              * Disappointment because what was in it for me was the potential to discover an outstanding amplifier which truly released the sonic potential of the Harbeth RADIAL cone. So I've been deprived of that discovery - or not maybe.
                              Alan A. Shaw
                              Designer, owner
                              Harbeth Audio UK

                              Comment


                              • The design levers available to an amplifier designer?

                                Clearly there is no comprehension at all of what goes on inside an amplifier's case. So let's compare the variables that the speaker designer (or car designer, microphone designer: all mechanical systems) have to play with and balance into some sort of uneasy compromise, and bring that product to market. As no two design briefs are the same, no two cars are the same, nor speakers nor microphones. Not only will there be individual piece-by-piece variations due to small but uncontrollable variations in parts used and their assembly but the overall balance of mechanical parameters will vary according to the designer's target. So you can have a car that glides over the road (a Rolls Royce) or a car that grips the corners like glue ans where you can feel every bump. But the designer cannot deliver a car that simultaneously glides and grips like glue. The design of any mechanical system is about making choices and prioritising them as the market requires.

                                How about electronic systems? Tuners, amplifiers, CD players, DACs, sound cards and so on. Let's compare. How much flexibility does their designer have?

                                A quick first-thing-that-comes-to-mind list of variables that (electro) mechanical (speakers, microphones etc.) has to play with and optimise for the market need:
                                1. Electro-acoustic efficiency from sound in/out to electricity
                                2. Mass of the moving parts
                                3. Diameter of the moving parts
                                4. Edge termination of the moving parts to allow them to move yet return to a neutral rest position aka spring compliance
                                5. Diaphragm thickness
                                6. Diaphragm shape
                                7. Diaphragm material
                                8. Acoustic properties of diaphragm materials versus frequency
                                9. Temperature stability of all moving parts
                                10. Optimum adhesives to bond and stay bonded over time
                                11. Acoustic properties related to adhesive rigidity
                                12. Amount of and exact location of glues and how to terminate a glue thread without blobbing (adding weight)
                                13. Fundamental resonance of the mass of the diaphragms bouncing on the air stiffness in the cabinet
                                14. Port tuning for amplitude, frequency and Q
                                15. Magnetic linearity with increasing power
                                16. Distortion minimisation
                                17. Effect of ambient temperature esp. on bass performance
                                18. Flatness of frequency response from individual drivers
                                19. Out-of-band unwanted peaks and troughs - avoidance or minimisation
                                20. Crossover, selection of optimum crossover frequency
                                21. Shape of crossover slopes below, at and above crossover frequency
                                22. Physical position of crossover components on the PCB to minimise magnetic interaction
                                23. Power durability in use with the customer over years
                                24. Cabinet damping on panel surfaces
                                25. Cabinet damping in the air cavity in-box
                                26. Method of attachment of drive units to cabinet and considerations of opposing forces and resonance avoidance

                                and so on. That's just for starters. There are probably over one hundred understood physical parameters which have to be simultaneously optimised by the designer, to fulfil his market needs even in the most humble, inexpensive speaker.

                                Now let's compare the levers of influence that the electronics designer has access to, and can apply to his design. It's a very short list indeed. The reason is that, unlike the speaker transducer which is an open-ended system (meaning, electricity is transformed to sound to one degree of efficiency or another) the amplifier is a closed-loop system. There is no conversion from one form of power to another (electrical energy to sound energy or sound energy to electrical energy): the amplifier works only in the electrical domain. The function of the amplifier is to a-m-p-l-i-f-y whatever voltage appears at the input socket into a bigger voltage at the output socket. That's it. That's all it has to do. Nothing more, and hopefully nothing much less. It is dumb. It does not know whether music or test tones are at the input terminals. It does not care whether it is Pink Floyd or pink noise it has to amplify. It is a brainless, obedient, robotic servant.

                                So what variables does the amp designer have to play around with? Well, he is chronically handicapped by two absolutely paramount, essential, life or death requirement:
                                1. Circuit stability over hours, days, years i.e if the amp fails it will destroy the speakers and/or catch fire
                                2. That the output must be directly correlated with the input i.e. if Mozart is appearing at the input terminals, Led Zeppelin is not appearing at the output terminals

                                So, with those overarching mandates the design begins. Presumably the prudent designer would start with a sketch of a simple block diagram that would increase the signal in two or three steps from the very small input voltage to a suitable one to drive a speaker - the so called 'gain structure' of the amp. Let's suppose that we needed 50v at the speaker terminals from a phono input of 50mV ... we'd need to increase the gain by (50/0.05) = 1000 times, also known as 60dB. We'd probably have a low-hiss input stage that increased the gain by 50 times and then a heavy duty output stage with a gain of 20 times, or whatever the designer wished for. The primary variable that the amp designer has available to him is the gain of those two stages (50x and 20x) can be set by the relationship between two resistors in the feedback loop, at a cost of about $0.02. This is the amplifier designers orbit of influence because whilst he may have dreams of exotic circuitry (because, as a creative person he's curious about new design approaches) he has to work within the two paramount requirements of circuit stability and input-output correlation. And we all know that the more complex a design becomes the more parts there are waiting to fail.

                                These paramount requirements mean that every component added to the design must be justified. If one capacitor will do the job, will two degrade long term reliability? Can adding components beyond those absolutely needed to perform the gain-up function be expected to improve the 'sound' of the amplifier? Fantasically unlikely because if they did, the amp had not been initially designed within the constraint of 2, the mandate of input-output correlation. Remember that unlike the speaker (or mic) where there is a transformation from sound into electricity making measurement tricky and hence introducing a big subjective element, the input and output of the amp can be directly compared since they are both electrical. They are both in the same domain. They can be both measured with the exact same equipment and directly compared, volts-in compared with volts-out.

                                Let us repeat the speaker designers design variables list again and remove from it those elements that the amp designer doesn't have and see what's left ....
                                1. Temperature stability of all (moving) parts
                                2. Distortion minimisation
                                3. Effect of ambient temperature
                                4. Physical position of (crossover) components on the PCB to minimise magnetic interaction
                                5. Power durability in use with the customer over years

                                We must add to that concerns about ventilation and electrical safety.

                                But the essential point is this: because electronic equipment such as amplifiers have no moving parts, their designer is not concerned with balancing the physical properties of moving parts such as mass, springiness and damping. And the 'personality' and sonics of every electro-mechanical system is directly and inextricably bound up with weights and compliance of the moving parts. Any system without moving parts is most likely to be free of the coloration that those moving components inevitably introduce.

                                As amplifiers have no moving parts and their gain is set by tiny resistors, is it really credible that there can be night and day differences in sound quality? No. Subtle ones surely, but they must be exceedingly small indeed or the test equipment could reveal them in the output when not present at the input.
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

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